Dropped it off at the indy shop in Raleigh yesterday afternoon for them to diagnose and fix today. They performed a smoke test and noted a large vacuum leak, replaced the DISA valve unit. Retested and found no more leaks. Total cost was near $497, including the $95 diagnostic charge and $240 for the part- it fails so regularly that they keep it in stock. I asked to see the old part; it had disintegrated upon removal but it was surprisingly filthy and def looked beyond its life. So far the car drives fine, if anything a drop in fuel consumption. Guess I need to cool my jets a bit on the backroads...the day before I'd been playing catch up with a E93 M3.